I. Samples of milk from one-hundred-andforty-two mares have been analysed for the purpose of determining the percentage of solids, protein, fat, lactose and ash. II. Of this number, thirty-eight samples were taken during the period of colostrum secretion and one hundred and four were colostrum-free milks. III. The average composition of the milk of British mares has been found to be in close agreement with that of Continental mares. The only marked difference is in the percentage of ash. IV. The average percentage of ash in the milk of Continental mares is 0.38 and in the milk of British mares 0.51. It has been-found that in the lighter British breeds (Ponies and Thoroughbreds) the ash content is similar to that of the continental mares, whereas in the heavier breeds (Clydesdales and Shires) the percentage of ash is appreciably greater. V. With the exception of the mineral content, there are no marked differences between the milks of the various British breeds. VI. Included in the samples examined were some from mares whose foals were not thriving; some of these milks were found to be abnormal. VII. The occurrence of oestrum in the mare commonly causes nutritional disturbance in the sucking foal. VIII. Milk with a high percentage of fat is unsuitable for foals, and mares that secrete milk of this nature do not rear their foals satisfactorily. IX. On the other hand,. foals appear to thrive well if the milk contains very little fat. X. The percentage of lactose in mare's milk is fairly constant. When divergence from the normal occurs, a slight excess does not appear to be harmful. Foals do not thrive when the milk contains much less lactose than is normally present. XI. Aged mares secrete milk that is normal or with a tendency towards richness. XII. The colostrum of mares has the same characteristics as the colostrum of cows. XIII. Two samples of "Witches Milk" (Hexenmilch) obtained from fillies born with fully functioning udders were analysed and in each case the milk was found to have practically the same composition as normal milk.